The present invention relates to a method of measuring a solid matter mass flow during conveying solid matter-gas suspensions into their conduits, particularly conveying in a dense stream with an increased pressure, such as for example during conveying of dusk-like fuels to gasification reactors operating at high pressure.
In conditions of a wide range of a fuel program, gasification of dust-like fuels with oxygen as gasifying medium in form of a flame reaction has been recognized as particularly advantageous. In many cases this gasification process runs with a high pressure, for example with a pressure of 3 MPa. Technological processes are known, for example as disclosed in the patent DD WP No. 147,188, in which the dust-like fuel is brought via a sluice system to a sufficient pressure and subsequently supplied in suspended condition in a carrier gas stream via supply conduits to one or several burners of the gasification reactor. As disclosed in this paper, it is desirable to retain the dust concentration in the carrier gas stream at an extreme height. Thus, for example, the ratio of the solid matter to the carrier gas-voluminous stream (relative to the working temperature and the working pressure) is adjusted greater than 300 kg/m.sup.3.
For the efficiency of the process and the technical safety of the device it is required to measure and regulate the quantity of the dust-like fuel supplied to a burner of the gasification reactor per time unit. If is known from DE-OS No. 2,556,957 to work with several intermittently operating pressure supply containers and to supply the dust-like fuel from these containers via a common supply conduit to the burner of the gasification reactor. In this case the pressure supply container can be supported, for example, on weight-measuring cells and the dust discharge from the supply container, and thereby the dust quantity supplied to the burner, can be determined per time unit. This method fails when several simultaneously or individually monitored supply conduits extend from a pressure supply container to the respective burners, or when a continuous solid matter stream is received from a pressure supply container which is periodically filled via suitable sluices or solid matter pumps.
It is also known to use a measure for the dust quantity stream the pressure drop of the dust-carrier gas suspension at a venturi nozzle installed in the supply conduit, as disclosed in the DE-OS No. 1,433,327, or over a predetermined length of the supply conduit, as disclosed in the publication K. R. Barker et al., "Pressure Feeder for Powdered Coal", Industrial and Engineering Chemistry, 43 (1951) par. 1204-1209. In addition to the fact that the installation of a throttling location such as a venturi nozzle during the supply of dust-carrier gas suspension with high solid matter concentration brings the danger of the operational stoppages because of clogging, the relation between the pressure drop and the dust quantity stream is determined by a plurality of further influencing values, such as geometry of the measuring device, a type of the solid particles to be supplied (grains, grain shape, surface properties, hardness, density), the relation of solid matter quantity to carrier gas volumes and the operational condition of the carrier gas at the measuring location. This method is connected with voluminous calibration work, so that such a measurement is used as a rule only as a tendency measurement.
It is also proposed to measure the carrier gas stream prior to loading with the dust-like fuel and the density of the dust-carrier gas suspension in the supply conduit and to calculate by suitable calculations the dust mass stream, the dust mass supplied per time unit, wherein as additional input values the density of the solid matter particles and the density of the carrier gas are introduced, as disclosed in the DE-OS No. 2,757,032. This method fails, however, when it is used with high solid matter concentrations, in specifically small carrier gas voluminous streams. Even if it is possible to cope with the problems of exactly measuring of small gas voluminous streams at a high pressure or the losses by leakages or by additional small carrier gas quantities supplied, for example, for spraying pressure measuring locations in the conduit, there take place in the sense of the instantaneous value in this conduit considerable differences between the carrier gas voluminous stream at the measuring location prior to the loading with dust and the calibrated carrier gas voluminous stream in the supply conduit. These differences are conditional to the pressure equalization process between the dust supply containers under pressure and the supply conduit which result from the sluice operation for filling of the supply container and from the small pressure variations in the entire system. These differences can be neglected when large carrier gas quantities are introduced for supplying the dust, so-called "thin" stream supply. In condition of a dense stream supply when, for example, a brown coal dust-carrier gas suspension with a concentration of 500 kg of the brown coal dust per m.sup.3 of the carrier gas is transported, these differences reach instantaneously the dimension of the entire carrier gas stream, so that the important instantaneous value of the dust mass stream calculated from the carrier gas stream and density of the suspension for the operation and the technical safety of the gasification reactor possesses considerable errors. Finally, the method of the DE-OS No. 2,757,032 cannot be used when several supply streams to be separately regulated and monitored exit from a pressure supply container and the entire carrier gas quantity is supplied as a uniform stream to the supply container.
A method disclosed in DE-OS No. 2,554,565 is also used for a thin stream-supply system, in accordance with which as a guiding value for regulating the dust mass stream a product is drawn from the solid matter density at the measuring location and the difference between a carrier gas voluminous stream and a comparison value is determined. Without further analysis, this method does not provide for a quantitative expression for the dust mass stream. Absorption measurements are used as measuring methods for the solid matter density in the dust-carrier gas suspension, during passage of electromagnetic waves through the suspension and measurements of the electric capacity of the dust-carrier gas suspension between two suitable electrodes is also proposed, as disclosed for example in the DE-OS No. 2,711,114.
Further methods are known for measuring the speed of the solid matter particles in an optical path; with the aid of addition of radioactive tracing substances; and by measuring the pulses of the solid matter stream, or in other words, by measuring the force which is applied by the solid matter stream upon a sensor extending into the stream. It has been shown that the optical measuring method, such as disclosed in the patent DD-WP No. 142,606 is not suitable for solid matter-carrier gas suspensions with very high solid matter concentration and high fineness.
Measuring methods with radioactive tracers are well suited for conducting individual experiments, but encounter some difficulties for continuous operation because of the ray protection and continuous supply and dosing. It is almost impossible to solve these problems if economic aspects are taken into account. Finally, there are measuring devices which operate with pulse methods, such as disclosed, for example, in the Publication Weber, "Aufbereitungstechnik" 7 (1965), p. 603-613. These devices are failure-susceptible in the event of high solid matter concentrations and lead to obstructing of the supply conduit by the sensor insertable into the solid matter stream. The obstructing danger is especially great when the solid matter contains fibrous particles as is the case with several sorts of brown coal dust.